1. Field of the Invention
This invention relates generally to semiconductor processing, and, more particularly, to a method for wafer-less qualification of a processing tool.
2. Description of the Related Art
The technology explosion in the manufacturing industry has resulted in many new and innovative manufacturing processes. Today""s manufacturing processes, particularly semiconductor manufacturing processes, call for a large number of steps that must be accurately executed to produce useful semiconductor devices. To maintain proper manufacturing control, a number of inputs are generally used to fine-tune the steps.
The manufacture of semiconductor devices requires a number of discrete process steps to create a packaged semiconductor device from raw semiconductor material. The various processes, from the initial growth of the semiconductor material, the slicing of the semiconductor crystal into individual wafers, the fabrication stages (etching, doping, ion implanting, or the like), to the packaging and final testing of the completed device, are significantly different from one another and specialized to the point that the processes may be readily performed in different manufacturing locations that contain different control schemes.
Among the factors that affect semiconductor device manufacturing are wafer-to-wafer variations that are caused by manufacturing problems that include start-up effects of manufacturing machine tools, memory effects of manufacturing chambers, and processing tool qualifications. One of the process steps adversely affected by such factors is rapid thermal processing (RTP) of semiconductor wafers.
Generally, rapid thermal processing (RTP) comprises quickly increasing the surface temperature of a wafer for short periods of time. For example, rapid thermal processing is used to thermally anneal a wafer, which generally takes place after an ion implantation process. During ion implantation, a surface of a wafer is bombarded with either N or P type dopant atoms, and as a result of the implantation, the crystal lattice of the semiconductor wafer may become damaged. The anneal step utilizes rapid thermal processing to recrystallize the silicon, which is required to produce functional semiconductor devices (e.g., memory, microprocessors, etc.) The wafer may be annealed by quickly ramping up to a desired processing temperature, holding the processing temperature for a desired period of time, and cooling the wafer back to room temperature in a matter of seconds. Although exact temperatures and times may vary depending upon the particular annealing process, the surface of the wafer may be heated to approximately 1000xc2x0 C. for 5 to 30 seconds.
Rapid thermal processing may take place in a processing tool that is specially designed for high temperature processes. Such a processing tool is typically qualified, through a qualification process, to ensure the tool is operating in a predictable predetermined manner. Generally, it is desirable to subject production wafers to substantially the same manufacturing conditions, such that the resulting semiconductor devices (e.g., memory, microprocessors, etc.) have substantially the same performance characteristics (e.g., speed, power, etc.) Moreover, periodically subjecting the processing tool to a qualification process may be useful to ensure that the processing tool is operating in a predefined state. If it is determined from the qualification process that the processing tool is not operating as expected, the tool may be taken out of production and corrective action may be initiated.
One method currently used to qualify a rapid thermal processing tool is to process temperature sensitive monitor wafers (i.e., test wafers) through the processing tool and measure the post-process characteristics of the monitor wafers. Depending upon the particular process or the particular semiconductor devices being manufactured, the monitor wafers may be subjected to a variety of processing tool qualification recipes. For example, with high temperature processes (e.g., 1100xc2x0 C. and above), the monitor wafers may be placed inside the rapid thermal processing tool and subjected to an oxide growth process. Once grown, the thickness of the oxide layer may be measured, and from this data, the current state of the processing tool may be determined. For example, the operating temperature of the processing tool may be approximated from the thickness of the oxide layer.
To qualify medium temperature processes (e.g., 800-1100xc2x0 C.), the monitor wafers may be implanted with a dopant material, placed inside the rapid thermal processing tool, and partially annealed. Once partially annealed, the resistivity of the monitor wafers may be measured, and based on the collected data, the current state of the processing tool may be determined. For example, if the measured resistivity is less than an expected value, the processing tool may be operating too hot, and if the measured resistivity is greater than an expected value, the processing tool may be operating too cool.
Typically, rapid thermal processes are very sensitive to time and temperature. To ensure that the processing tool is operating within a predefined state, the processing tool may be qualified on a regular basis. For example, in one embodiment, the processing tool may be qualified every 24 hours. Alternatively, for critical processes, the processing tool may be qualified multiple times within a 24 hour period.
To produce accurate and reliable results, a qualification recipe may require many monitor wafers to be processed by the processing tool. Unfortunately, a typical monitor wafer may be used only once and must be discarded after a single use. The cost of these test wafers may be a large and substantial expense in semiconductor manufacturing. In addition, qualifying processing tools with monitor wafers introduces additional unnecessary external factors to the process, such as test wafer preparation, test wafer measurements, and nonuniformity between test wafers.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the invention, a method for performing a wafer-less qualification of a processing tool is provided. The method includes creating a wafer-less qualification model for the processing tool. Qualification data is generated from the processing tool during a wafer-less qualification process. The qualification data is compared with the wafer-less qualification model. The processing tool is determined to be operating in a predefined state based on the comparison of the qualification data with the wafer-less qualification model.
In another aspect of the present invention, a system is provided. The system includes a processing tool, a plurality of measuring devices, and a process controller. The processing tool is adapted to being qualified using a wafer-less qualification process. The plurality of measuring devices are adapted to measure data during a wafer-less operation of the processing tool. The process controller is adapted to create a wafer-less qualification model of the processing tool, receive qualification data from the processing tool, compare the qualification data with the wafer-less qualification model, and determine if the processing tool is operating in a predefined state based on the comparison of the qualification data with the wafer-less qualification model.